1. Field of the Invention
The present invention relates to a multilayer sheet and also a back sheet for solar cells and a solar cell module prepared by using the multilayer sheet. More specifically, it relates to a multilayer sheet having a polyvinylidene fluoride-based resin layer and also a back sheet for solar cells and a solar cell module prepared by using the same.
2. Description of the Related Art
As solar cell modules are used outdoors for an extended period of time, for assurance of mechanical strength and prevention of degradation under the environment atmosphere, generally, they have a configuration in which the solar cells are sealed with a synthetic resin, covered with a transparent strengthened glass on the sunlight-exposed face and protected with a back sheet on the opposite face. The back sheet for solar cells used then is for example a laminate of an aluminum foil and a resin film or a laminate of multiple resin films different in composition (see, for example, Patent Documents 1 to 5).
For improvement of weather resistance, Patent Document 1 proposes a rear face-protection sheet for solar cells in the configuration of a laminate of polyethylene-based resins each having a particular density or a laminate of a polyethylene-based resin having a particular density and a thermoplastic polyester resin film. Alternatively, Patent Document 2 proposes an integrated back sheet having an external surface film and a moisture-proof film adhered with an adhesive based on an ethylene-vinyl acetate copolymer. The back sheet described in Patent Document 2 employs a laminate film consisting of a base film and an inorganic oxide coating film formed on the surface thereof as its moisture-proof film and a fluoroplastic film as the external surface film.
Alternatively in the rear face-protection sheet for solar cell modules described in Patent Document 3, a heat-resistant polypropylene-based resin film containing a colorant additive, an ultraviolet absorbent, and a photostabilizer is laminated on both faces of a base film having a vapor-deposited film of an inorganic oxide. Alternatively in the rear face-protection sheet for solar cell modules described in Patent Document 4, a fluoroplastic layer having a halogen mass ratio of 50% or more is laminated on one or both faces of a polyphenylene ether base sheet for improvement of flame resistance.
Generally in such a multilayered back sheet for solar cells, multiple films are laminated with an adhesive. Alternatively, Patent Document 5 proposes use of a hydrolysis-resistant, electrically insulating, and water-blocking acrylic adhesive in lamination of a polyester base material, a polycarbonate-based base material, a fluorine-based base material, or an acrylic-based base material.